From: Andreas Dilger <adilger@home.com>
Date: Mon, 17 Jan 2000 21:34:55 -0700 (MST)
On the other hand, it shouldn't be any problem to have a user-space
tool to check that the backup superblock/GD copies are consistent
with the primary In fact, the ext2online user-space does a copy of
the primary superblock/GD to all of the backups after the the kernel
resize code is finished. These backup superblocks and group
descriptors are never in use while the filesystem is mounted, so it
is safe to write into them.
Maybe e2fsck can check that the first 2 superblocks match at boot time,
and leave the rest to user-space code, or until the filesystem is unmounted
or e2fsck is run that modifies the filesystem.
This doesn't make any sense. The backup superblocks are useful in case
the primary superblocks get trashed. The kernel never updates the
backup superblocks, since (a) this minimizes the chances the backup
superblocks will get trashed, (b) the parameters that are most criticial
for recovering a filesystem after the primaries get trashed don't change
normally (i.e., size of the filesystem, blocksize, etc.), and (c)
updating the backup superblocks would take extra time.
So merely comparing the first two superblocks can't tell you much
except that the primary superblocks haven't gotten smashed. It doesn't
tell you anything about the health of the filesystem as a whole.
- Ted
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